The present invention relates generally to a system and method for motor control, and more particularly, to a test module for use with a subunit for a motor control center. The test module provides equipment connection points and voltage test points, so that a user can monitor internal conditions of the subunit when the subunit is installed into the motor control center. In one embodiment, the system and method described herein provide for connection of external accessories, such as motor meggaring devices, voltage/current testing equipment, and motor wellness units, to internal test points of the subunit, without a need for removing or opening the motor control center subunit.
A motor control center is a multi-compartment steel enclosure with a bus system to distribute electrical power, on a common bus system, to a plurality of individual motor control units mountable within the compartments. The individual motor control center subunits are commonly referred to as “buckets” and are typically constructed to be removable, pull-out units that have, or are installed behind, individual sealed doors on the motor control center enclosure. These buckets may contain various motor control and motor protection components such as motor controllers, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and similar devices for electric motors. The buckets connect to the supply power lines of the motor control center and conduct supply power to the line side of the motor control devices, for operation of motors. Motor control centers are most often used in factories and industrial facilities which utilize high power electrical motors, pumps, and other loads.
Typically, when installing or removing motor control center buckets, the power supply lines are connected. To remove such a bucket, a deadfront door of the bucket or of the motor control center is opened and an operator manually pulls on the bucket to separate the primary disconnects, or “stabs,” from the bus system, thereby disconnecting the power supply. Installation of a bucket is accomplished in a similar manner, wherein the operator manually pushes the bucket into a compartment of the motor control center to engage the bucket stabs with the bus system, thus connecting the system to supply power. The line connections or stabs may be difficult to maneuver manually when an operator is supporting the entire bucket or when the stabs are not visible.
Attempts have been made to improve upon the manual installation and disconnection of motor control center buckets and supply power connections from live supply power lines, risers, and/or a vertical bus of a motor control center. Other systems have employed pivotable handles inside the buckets to pivot line connectors to and from supply lines. However, many of these systems require that the bucket or compartment door be open to manipulate the handles and line stabs.
Similarly, once a bucket has been fully installed and/or sealed in place in a motor control center, it becomes difficult to monitor conditions inside the bucket without disconnecting the bucket and removing it from the motor control center. For example, in some systems, to test line or load voltages and currents, contactor or starter voltages and currents, and control signals, doors or seals of the bucket would need to be opened, or the bucket would be partially or completely removed.
It would therefore be desirable to design a motor control center bucket assembly that overcomes the aforementioned drawbacks. Thus, it would be desirable to provide for remote connection or disconnection of the line stabs of a bucket to the power supply lines or bus of a motor control center from a distance. In the event of an arc or arc flash, any heated gas, flame, and/or the arc itself should preferably be contained behind the bucket compartment door or “deadfront.” It would further be desirable to include a test module which could convey conditions inside a fully installed bucket to an operator via an interface on an external side of the bucket.